Warren,

Did the van start without problem before it sat for a month?  I would first
check to see that the battery is fully charged.  It takes a lot of juice to
start one of these diesels.  Especially in colder weather and as they get
older and the engine loses compression.  If the engine in fact has lost its
prime, it means that the fuel pump/distributor is sucking in and pressurizing
air instead of fuel.  The fuel must be delivered to the fuel injectors under a
considerable amount of pressure (without any air pockets) in order for the
engine to start.  There are two likely suspects here: the fuel line between
the fuel filter may be allowing air to seep in. The Fix: Replace the fuel line
with regular fuel line available at any parts store, Be sure to clamp the hose
Securely!  OR the seal on the main shaft of the fuel pump has deteriorated and
is allowing air into the system.The Fix:The seal is available and costs
approximately $12.00 or you can replace the entire pump for considerably more
$$$$$!
    Once you have stopped the flow of air, you can reprime by cranking the
engine.  Again make sure you have a strong battery.
I hope this helps you, please let me know if I can be of further assistance.

Chris
86 Westy